Combobox dropdowns cut off when screen height is shortened

I am unable to access all of the options in a combobox when my screen height (or IFrame height) is shortened to a small enough size. See the attached image of the GXT showcase, when the browser (Firefox) is compressed to a shorter height. You have the same effect when you are in an IFrame (portlets, etc..).

GXT 2 had a setMaxHeight option for ComboBox, which might provide a workaround this problem, but this is missing from GXT 3.